Now Is the Time to Open Your Heartby Alice Walker224pp, Weidenfeld & Nicolson, £12.99

During the first chapter of Now Is the Time to Open Your Heart, I thought we were in for a treat. Alice Walker's new novel opens with a rather funny scene in which a 57-year-old woman, Kate Nelson, who has just renamed herself Kate Talkingtree, finds herself losing faith in the middle of a meditation weekend. She is listening to a talk by a guru who is telling the mainly white, middle-class meditators that "hot" revolutions can never succeed, that the only way to success is through the "cool" revolution initiated by the Lord Buddha. "Easy enough for him to dismiss the brown and black and yellow and poor white people all over the globe..." thinks Kate, realising that she has reached "an impasse on the Buddhist road".

Great, some readers will start to think. Walker is going to spear the decadence of western New Age philosophies. Her previous novels have been so good at showing the contradictions and complexities behind fashionable liberal assumptions. Can you forget how her fierce novel Meridian skewered the way that white and black people interacted in the civil rights movement? Or the way Possessing the Secret of Joy made anyone who indulged in cultural relativism about female circumcision truly ashamed of themselves?

But this novel, sadly, is not trying to be fierce or subtle about New Age thinking. On the contrary, it is a simplistic book that hardly becomes a novel, because it stays on the level of mere rhetoric for so much of the time. Walker takes Kate away from her meditation retreat, to be sure, but only to push her into a couple of other religiose epiphanies, one on a river journey and one on a long-winded jungle retreat. There she learns, in company with a few other miserable people from north America, that "the saving of the planet can be done really easily. All that is required is that everyone becomes as one mind."

While listening to this kind of waffle, Kate and her fellow retreaters have to take medicine that makes them vomit, wear nappies in case the diarrhoea gets too bad and share their miseries and tedious dreams with one another, in order to "feel the fucking pain to the core" until they can find themselves "feeling an inner space. A clarity".

Perhaps the real problem here lies in Kate Talkingtree herself as a protagonist. Walker's most memorable heroines (Celie in The Color Purple, Tashi in Possessing the Secret of Joy) were vulnerable and often wrong, and the novels were about their journeys into self-realisation. Their particular voices and experiences stayed with the attentive reader for ever. Kate is a one-dimensional character, smugly attending to her spiritual superiority rather than any outside realities. "She decided not to worry about piranhas or crocodiles but to concentrate instead on her inner peacefulness", we hear at one point, but inner peacefulness is not as fascinating to read about as it might be to experience.

The plot, thankfully, does not only stay in the forest with Kate, her vomiting friends and their inner space. It also flicks to Hawaii, where Kate's lover is on holiday. He has found an old girlfriend there who is mourning the death of her son, and for a time these scenes have the emotional rawness that is one of Walker's greatest strengths. But then, as if infected by Kate's parts of the novel, even these sections descend into sloganeering about the spiritual poverty of modern life, and how this poverty could be cured if we only ate the right things: "We will have no future eating the slops the masters have brought... It is all about food..."

When Kate's boyfriend returns from Hawaii, he too seems to have undergone an epiphany, which results - excitingly or disappointingly, depending on how much you buy into the idea of purification as revolution - in his trying to give up smoking. The two of them then plan a wedding, or rather a "circle to celebrate sharing our life together", and Kate uncovers the Buddha that she keeps in her altar room. Flickers around the end of the book suggest that this is occurring around the time of September 11. As a kind of essay on the way we should respond to that atrocity, I can imagine that this heartfelt, well-meaning book about spiritual renewal will touch many readers; but as a novel it is a great disappointment.